On Mon, Jul 30, 2012 at 9:51 AM, Guido van Rossum <gu...@python.org> wrote: > > Also, I have a few content quibbles: > > - Is it really worth flagging a negative return value with ValueError? > I'd just as well clip this to zero. What's the worry? That the > computed value is wrong? But it's only meant to be a hint, and why > would -1 be any more wrong than e.g. 1000000000? > > This was done for consistency with len(), I'm not particularly attached to any behavior.
> - Did you mean to define operator.length_hint()? > > Of course :) > - The default can be zero with no semantic impact, so I think there's > no need to require the caller to specify a default. > > I suppose that's fair. > - Most importantly: calling len(obj) and catching TypeError can only > be a substitute for the real implementation, which IMO ought to check > for the presence of a tp_len slot. Alas, checking hasattr(obj, > '__len__') doesn't quite cut it either, since this returns true for a > class object that defines a __len__ method for its instances (the > class itself doesn't have a length). Still, I worry that calling > len(obj) and catching all TypeErrors overspecifies the desired > behavior; what I *want* to happen is to check if there is a __len__ > method, and if so, call it and let any exceptions bubble through. It > may be best to add a comment explaining that am implementation doesn't > have to follow the letter of the Python code in the PEP, in > particular, if obj *has* a __len__() method but calling it raises an > exception, then length_hint(obj) may (ought to?) pass this exception > on instead of calling obj.__length_hint__(). > > Seems reasonable, rather than try to spec that out precisely in the pseudocode (aka Python ;)) a note like you suggest sounds good. > -- > --Guido van Rossum (python.org/~guido) > Alex -- "I disapprove of what you say, but I will defend to the death your right to say it." -- Evelyn Beatrice Hall (summarizing Voltaire) "The people's good is the highest law." -- Cicero
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